Not Applicable
Not Applicable
1. Field of Invention
This invention pertains to cooling systems for electrical panels. More particularly, this invention pertains to a bus cooling fan that is powered from the electromagnetic field generated by an electrical bus and that does not require external electrical connections.
2. Description of the Related Art
Electrical panels, such as switchboards and switchgear, are used in electrical power distribution systems. These panels typically contain circuit breakers, transformers, and instrumentation. The electrical connections between these internal components are made with bus bars, with one bus bar for each phase of the polyphase electrical system and another bus bar for the neutral conductor, if there is one. The current flowing in many electrical power distribution systems is oftentimes high, resulting in heating of the bus bars and other components in the electrical panels. It is common to cool these components with an externally powered, electric cooling fan, which forces air to circulate through the panel. Using an externally powered, electric cooling fan necessitates an external power source and wiring.
Externally powered, electric cooling fans are typically driven by single-phase induction motors. These motors typically have a wound stator and a squirrel cage rotor, which rotates and drives the fan blades. Single-phase induction motors require some means of applying torque to the rotor in order to overcome inertia and start rotating. Various methods are known for starting single-phase induction motors. For example, the stator may use a shaded pole, where one-half of each pole is surrounded by a short-circuited winding called a shading coil. Another example is a split-phase motor, where the stator has two windings, one of which is an auxiliary winding which has an out-of-phase current relative to the other winding. A capacitor can be wired in series with the auxiliary winding of the split-phase motor. If used, the capacitor can be switched out of the circuit after the motor reaches a certain speed, or the capacitor can be left in the circuit and used to improve the motor""s power factor.
According to one embodiment of the present invention, a cooling fan without external electrical connections, provides cooling for polyphase bus bars in an electrical panel. The cooling fan operates as an induction motor in which the fan blade supports act as a rotor and the bus bars act as a stator.